High frequency electrical oscillation generator and amplifier



Jan. 22, 1935. E. GREEN ET AL 1,988,487

HIGH FREQUENCY ELECTRICAL OSCILLATION GENERATOR AND AMPLIFIER Filed July 19. 1932 OUTPUT CIRCUIT ff/ OME OUTPUT c/ncun 3 w INVENTORS ERNEST GREEN V FREDERICK (:AWN R055 5,1555% A'TTORNEY Patented Jan. 22, 1935 men FREQUENCY ELECTRICAL OSCILLA- r 1 'rloN GENERATORIAN-DYAMBLIFIER 1 Ernest Green, Chelms'fori and E rfederickGawn Robb, panbury; England, assignors t'o'Radio a Gorporation ofAmerica; a corporation of Delaware Ata ama-l ar 19, 1 32; ..Se a No. 62336 I i 4 I p Thispinvention relates too high frequency circuit arrangements and has'for its object topm- 'vide an improved high .frequency circuit and,

-more,particularly, an improved circuit for. useon veryshort waves of the order of 30 metres orless wherein means areprovided for eliminatingoscil- .lations of undesired frequency.

As is. .well known, oneof the 1 difiiculties .experienced .inhigh frequency. oscillation generators and the-likeis that therei is. a liability forthe setting up of frequencies. other .thanthe desired or main oscillation frequency; and various proposals have been made for eliminating such undesired frequencies; For example. in thelprevious British PatentxNo. 148,447 vthesetting up'of. oscillations of an undesired frequency in a thermionic generator in which oscillations of either oftwo frequencies may be produced is preventedby the interposition of an auxiliary. condenser or inductance. or. resistance or: a separate circuit syn- .tonized. to the undesired frequency. Similarly, reference may be made tothe. previousLBritish patent specification .No. 148,445. Further, various proposals have been made to'elimin'atewhat are known as parasitic oscillations,.theseproposals consisting in the main ininserting dampingresistances in the probable path of parasitic oscillations. For fantiparasitic arrangements of this general kind, reference may be made toUnited States Patents Nos. 1,830,164, 1,787,309, and 1,954,589. r I

It has now been found that in short wave oscillation generating and amplifying circuits, there is a great tendency for the setting up'of parasitic oscillations when the constants of the circuit are such that the natural frequency of such parasitic oscillations equals or approximates to a harmonic of the 'mainor desired oscillation-frequency; The object f the present invention is to provide means for avoiding-this particular diflic1'1ltyj-and according to this invention adiustable'reactive means are provided for altering the natural frequency of the circuit'generating or tending to generate parasitic. oscillations so that the natural frequency is-n'ot or doesnot approximate toa harmonic of themain oscillation frequency.

The present invention may be employed in conjunction with any other means for suppressing parasitic oscillations. v i V Figure '1 of the accompanying drawing illustrates one way of carrying out the invention as applied to an amplifier consisting of a single thermionic valve to whose grid circuit are applied the oscillations to be amplified, andas will be seen an added inductance, preferably variable,

is provided 3 in accordance. with theinvention in theparasitic oscillation circuit. Figure 2 represents avariationof this arrangement.- :Figure 3 illustrates I one away :iof. applying the principles of the. presentinventi'on'to a two valvecircuit, and

--Figures .41and.5 are furtherlembodimentssof th invention as'appliedto two valve circuits. .pqReferring'to Figurel which only shows those parts of the circuitrevelent. to :the present-in- Vention-the .amplifi'erzvialve circuit comprises a .:valve.-1-having 'in'its; grid circuit the usual coil 2- .qforq-the applicationpof the .fdri've and having in itsplate'circuita parallelresonant circuit3, 4, tuned to the main or; working frequency. The end of this resonant circuit remote from the plate -is connected to the. grid; through a neutralizing condenser. 5 and (in accordanceqwith this inuventionl-a small-variable inductance 6 in series. This smallvariable inductance is adjusted in value gto' remove:parasiticroscillations.' I v In a variation of thisarrangement the small inductance is as shown inthe accompanying Fig- .ure 2 shunted by a tuning condenser 7 in series witha resistance 8 so that the inductance, condenser, and.-,resistance together constitute. a .dampedtuned-circuit. The provision of the resistance renders the adjustment less critical.

In a furtherarrangement'shown in the accompanying-Figure-B an amplifier consists of two .valves 1, l whose platesare connected together 7 through a parallel tuned circuit 3, 4,anode feed .being appliedto. the mid point of the coil of this circuit. The plate of each valve is also connected to. the grid of the otherrthrough a condenser 5 or, 5]- and small variable inductancefi or '6 in series with one another, the small variable inductancesbeing adjusted for the elimination of parasitics. The drive-is applied -via coil 2 as gshown tothe two grids at the junction points A of thesmall; variable inductances and the condensers in series therewith. If desired, the small variable inductance may be replaced by tuned circuits consisting each of inductance shunted by capacity andresitance in series, as in the single. valve amplifier shown in Figure 2. v

If desired, and as shown in the accompanying .Figures 4 and-5 .the adjustment devices'may be ina separateloop, circuit. In Figures 4 and 5 .the plate of-each,valve 1 or 1 is connected to the grid of the other through a condenser. Coupled to the two grid leads is a loop circuit across which parasitic eliminating adjustment means is symmetrically shunted. The coupling of this loopcircuit to the grid leads may be made as shown in Figure 4 by employing as the loop circuit a loop of wire or conductor 9 running parallel to the grid wires in such manner that the coupling thereto is equal i. e. the coupling to one grid wire is equal to the coupling to the other. The adjustment device comprises a resistance' 10 and'a condenser 11 inseries and" is connected symmetrically across the loop. In the arrangement shown in Figure 5 the coupling of the loop circuit containing the adjustrnent device to the grid wires is made by means. of coils; Inthis arrangement each gridwire contains a small coupling coil 12 or 12 coupled 'to iorielof a' pair of smaller coils 13 or 13' in theloopcircuit, d before, the adjustment device consists "of a condenser 11 and resistance 10in series connected 7 symmetrically across the loop; {The arrange ments shown in Figures 4and '5'," wherein the anti-parasitic adjustment devices are across a loop circuit, present the advantage that the ad- .justment devices which serve to varytthe. tuning -of1the circuit tendingto set up:parasitic'oscih lationshaveino reaction back-- on the :main oscillations while'at the sameltimethere is close coupling as regardszthe parasitic oscillations; L

Having now particularly described and ascertained the naturekof our said invention-andin what manner the same i is to be performed,l we declare that what we claim iszt- -xv1 1. A high frequency circuit i arrangement comprising an electron discharge: device having a control electrode and anf anode in circuit with a vtuned output circuit, a direct conductivec'onnection from one 'terminal of saidoutput circuit to said anode, a connection including a condenser from the other-terminal of said output circuit to said control electrode, said output circuitand connections having constants suchthat the natural frequency of parasitic oscillations' approximates a harmonic-of the desired frequencyi-and adustable reactive means included insaid last connection for preventing parasiticswhereby said natural frequency of the parasitic oscillations is altered to a value which does" not approxim'ate to a harmonic of the desired frequency.

2. An arrangement as defined in claiml; characterized in this, that said adustable-reactive -means includes a variable inductance. e

3. A high frequency circuit arrangement comprising an electron discharge device having a control electrode andan anode in circuit with a tuned outputcircuit, a direct conductiveconnection from" one terminal of'said output circuit to saidianode, a connection -including a condenser from the other terminal of said output circuit to said control electrode, said output circuit and connections having constants such that the natural frequency of parasitic oscillations "approximates a harmonic of thedesired Irequency',"and means comprising an inductance shunted by a condenser and a resistance in series" included in said last connection for preventing parasitics whereby said natural frequency of-the parasitic oscillations is altered to a value which does not approximate'to a harmonic of thedesired-frequency; l i s,

4. An arrangement asdefined in claim -3,'-characterized' in this, that said last' means comprises a damped tuned-circuit having'an-adjustable'infrom the other terminal of said output circuit to {said control electrode, said output circuit and .,,connections having constants such that the natural irequency of parasitic oscillations approxif' mate's'fa harmonic ofthe desired frequency, and djustablereactive means in circuit with said last connection 'for preventing parasitics.

6. A high frequency circuit arrangement com- ;prising an electron' discharge device having a control electrode and an anode in circuit with a tunedputput circuit, a direct conductive connection'from one terminal of said output circuit to -said' anode, a connection'including a condenser -fromlthe 'other terminal of said output circuit to said control electrode, said output circuit and connections having constants such that the naturalni'requency of parasitic oscillations approxi- --mates aa-. harmonic of the desired frequency, and

adjustable reactive means in circuit with said last 'connectio'nlfor preve'ntingp'arasitics, comprising a eparallel: tunablel loop circuit having a variable 'icondenser and au-resistance in series, and a con- Jnectiontin 'parallelwith said series combination of "condensenand resistance, saidloop circuit being --inductively=coupledto a connection which extends from said output circuit to said control electrode.

- -;.7; A':high frequency circuit arrangement comprising an electron discharge device having a con- :trol'electrode and an anode in circuit with a'tuned :output circuit, a direct conductive connection --from.one terminal of' saidoutput' circuit'to said -anode,'-aiconnection including a condenser from .the other terminalof said output circuit to said control-electrode, said output circuit and con- ,nections'having con-stantssuch' that the natural frequency of parasitic oscillations approximates a harmonio'oi the desired frequency, and adjustr able reactive zme'anszincircuit with said last connection :for. preventingparasitics comprising a :parallel tunable -.loop-.icircuit having a variable condenser, and a; resistance in series, and an in.- ductance'coil in parallel .with said series combination of condenser and resistance, said loop circuit. being inductively coupled through said in- ;ductanc'e coil tosaidsconnection'which extends 'rfrom said output-circuit to said control electrode. .8;;-'Ihe combinationzswith a push-pull circuit comprising-twoelectron discharge devices whose electrodes at, the junction points of'the neutralizing'. condensers, and the ;coils.-,

respective inductance I ERNEST GREEN. 7 {FREDERICK GA-WN ROBB. 

